Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to engine intake for combustion, further improving fuel economy.
In a typical canister purge operation, a canister purge valve coupled between the engine intake and the fuel canister is opened, allowing for intake manifold vacuum to be applied to the fuel canister. Simultaneously, a canister vent valve coupled between the fuel canister and atmosphere is opened, allowing for fresh air to enter the canister. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
As fuel temperature rises during hot weather conditions, vehicle motion and resulting sloshing of fuel within the fuel tank may cause transient slugs of vapor. These vapor slugs from the fuel tank may enter the engine intake during a purge operation and cause engine stalling. As such, when presence of vapor slugs is deduced, the ongoing purge operation may be discontinued to reduce the likelihood of engine stalling. However, this suspension of the ongoing purge operation may lead to an increase in emissions. Further, a subsequent purge operation may have reduced efficiency due to the delay in ramping up the subsequent purge operation to the level of the previous discontinued purge operation. Further still, if the canister is not purged as frequently as demanded, the vehicle may not meet desired standards in an emissions test (e.g. Federal Test Procedure).
The inventors herein have recognized the above issues and have developed systems and methods to at least partially address them. In one example, a method for purging a fuel vapor canister comprises, responsive to an indication of vapor slugs, reversing a direction of air flow through the fuel vapor canister in a vehicle while maintaining purge air intake at a vent line inlet. By reversing the direction of air flow through the fuel vapor canister, the vapor slugs may be adsorbed in the fuel vapor canister.
In another example, a system for an engine comprises a fuel tank, a fuel vapor canister comprising a fuel vapor canister buffer coupled to the fuel tank, the fuel vapor canister buffer arranged at a first end of the fuel vapor canister, a purge line coupling the fuel vapor canister to an engine intake via a canister purge valve, a vent line coupling the fuel vapor canister to a fresh air source, a canister vent valve coupled between the fuel vapor canister and the vent line, the canister vent valve operable between a first conformation and a second conformation, a reversing valve coupled between the fuel vapor canister buffer and the purge line, the reversing valve operable between a first conformation and a second conformation, and a controller having executable instructions stored in a non-transitory memory for, when canister purge conditions are met, drawing air through the fuel vapor canister with the canister vent valve in the first conformation and with the reversing valve in the first conformation, and in response to inferring fuel vapor release higher than a threshold vapor release from the fuel tank, drawing air through the fuel vapor canister with the canister vent valve in the second conformation and with the reversing valve in the second conformation.
For example, a vehicle system may include an evaporative emissions system including a fuel vapor canister. The fuel vapor canister may include a fuel vapor canister buffer arranged at a first end of the fuel vapor canister. When purge conditions are met, fresh air may be drawn through the fuel vapor canister and may be streamed along with desorbed fuel vapors via the fuel vapor canister buffer at the first end of the fuel vapor canister towards an engine intake. A canister purge valve may be opened to enable the purge operation. During the purge, if a presence of vapor slugs is inferred by indication of fuel vapor release higher than a vapor release threshold, the purge direction may be reversed. Herein, fresh air may be drawn through the fuel vapor canister buffer at the first end of the fuel vapor canister, and may be streamed through the fuel vapor canister. Due to the reversing of purge direction, the vapor slug arriving at the fuel vapor canister buffer from the fuel tank may flow through the fuel vapor canister along with the fresh air and may be adsorbed. The fresh air along with desorbed vapors may exit the fuel vapor canister via an end opposite the first end of the fuel vapor canister towards the engine intake.
In this way, adverse effects of vapor slugs on engine operation may be reduced. By reversing the direction of purge flow in response to the indication of vapor slugs, the purge operation may be continued while simultaneously allowing the vapor slugs to be adsorbed in the fuel vapor canister. Thus, an engine stall due to a sudden increase in fuel vapor may be reduced. Further, by maintaining the purge operation, the fuel vapor canister may be evacuated fully. As such, purge efficiency may be improved. Overall, the performance of the evaporative emissions system may be more robust and efficient.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.